The present invention relates to heterocyclic aromatic compounds containing 4,6-bis-trichloromethyl-s-triazin-2-yl groups, to a process for their preparation and to a photosensitive composition containing these compounds.
It is known to employ aromatic or heterocyclic compounds containing trichloromethyl groups as initiators for various photochemical reactions.
DE-A 22 43 621 discloses s-triazines that are substituted by one or two trichloromethyl groups and one chromophoric group and are suitable as photoinitiators in photopolymerizable compositions and as acid donors in a mixture with acetals that can be split by acid. These compounds also include those that absorb light in the visible region of the electromagnetic spectrum and act as photoinitiators. Their sensitivity in this region is, however, insignificant.
Similar compounds, in which an at least binuclear aromatic radical as a chromphoric group is bonded directly to the triazine ring, are disclosed in DE-A 27 18 259 (=U.S. Pat. No. 4,189,323).
EP-A 137 452 describes similar 4,6-bis-trichloromethyl-s-triazines that have an optionally-substituted styryl group in the 2-position. The absorption peaks of these compounds are mostly in the near ultraviolet region.
DE-A 28 51 472 describes photosensitive compositions that contain 2-halogenomethyl-5-vinyl-1,3,4-oxadiazole derivatives as photoinitiators.
DE-A 30 21 590 and DE-A 30 21 599 disclose halogenoxazoles that are substituted by trichloromethylphenyl groups and are suitable as photoinitiators, like the above-mentioned compounds.
Moreover, EP-A 135 348 and EP-A 135 863 (corresponding to U.S. application Ser. No. 06/651,116) disclose 1-alkyl-2-carbonylmethylene-benzothiazoles and similar heterocyclic compounds, that carry a trichloromethylphenyl group on the carbonyl group. These compounds also have their maximum sensitivity in the near ultraviolet region.
The known photoinitiators have a number of disadvantages. The reaction conditions for preparing many of these compounds are fairly drastic so that the yield is relatively low and the formation of undesired by-products that are difficult to separate is favored (for example, DE-A 22 43 621, DE-A 27 18 259 or 28 51 472). With many known initiators, the inadequate sensitivity makes it necessary to combine different initiator systems with one another.
Basically, most of the above-described initiators can be used to prepare photosensitive compositions, the sensitivity of which is good in the near ultraviolet region, but inadequate in the visible region. Upon exposure to conventional lasers emitting visible light of relatively low energy, the initiating action of these lasers is either nonexistent or only very slight. Moreover, it has been found that precisely the most sensitive of the known initiators do not have a storage stability that meets the requirements of practical application in photosensitive compositions, in particular in contact with copper surfaces.
Since an increased use of lasers, in particular, of argon or krypton lasers that have an emission between 450 and 650 nm and are employed as recording lasers, has to be expected in the future, highly photosensitive initiators and compositions must be provided, that exhibit adequate sensitivities in these applications.